Trucks for hauling open top containers are frequently provided with covering systems which cover the load being transported in order to either protect the load or prevent parts of the load from being blown out of the container.
Open top containers are formed as separable units which can be secured to the frame of a truck for transport or removed for use. For example, containers used to receive and contain trash at a construction site are generally only loaded onto a truck for transport. The trash containers all have a generally rectangular shape, but vary in loading capacity, usually from 10 cubic yards to 50 cubic yards. The containers vary in both length and height, with the sidewalls ordinarily ranging from 4-8 feet in height and 10'-35' in length. Most containers in use today are 4', 6' or 8' high and 21-23 feet long.
The covering systems in the past have most commonly relied upon a tarp which extends to cover the container and retracts onto a central roller bar or other spindle to a stowage position. The truck is usually provided with arms which are pivotally attached to the frame of the truck to swing over the container in extending and retracting the tarp. However, trash containers are typically overfilled with all kinds of trash to form an irregular load which may be heaped or have items protruding upward above the upper edge of the container or outward beyond the sidewalls along any part of the container. As a result, the arms may not be able clear the load.
The arms are generally driven by hydraulic cylinders in moving the tarp to cover and uncover the load. As a result, the arms may be damaged by trying to cover a heaped or protruding load which the arms do not clear. In addition, the arms extend along the sides of the truck and are thus susceptible to being struck as the truck is moved. As a result, the use of arms can lead to higher maintenance costs. Moreover, since the arms are generally spindly, they are frequently being damaged and left in an unusable state. In systems where the arms are broken or fail to clear the load, the operators must climb onto the containers and loads in order to extend and retract the tarp. Climbing onto the container places the operator at risk of injury by either falling from the container which could be a great height off the ground or onto the load which may have sharp edges. Use of hydraulic cylinders have also led to the arms striking or trapping an operator's arm or head as the truck arms are swung about the container and causing injury. The arms, particularly if bent outward by an earlier accident, have been known to strike objects and people as the truck is driven causing damage, injury, and even death.
Further, even aside from damage and injury concerns, the use of the pivoting arms can be a burden to the operator. For example, the arms are ordinarily adjustable in length to accommodate the different sizes of containers to be hauled. A manual adjustment of the length of each arm may therefore be necessary before the load can be covered. While some systems have hydraulics or other devices to effect adjustment of the arms, these systems tend to be complex, expensive, and/or require high maintenance.
To avoid the problems associated with the use of arms, other trucks have been provided with armless covering systems which are manually extended by a pull rope. These tarp devices have normally been attached directly to the container or a fixed structure so that the tarp must be drawn along the top of the container to the rear of the truck. To facilitate this operation, most of these tarps have rollers on the outside of a pull bar to ride along the top edges or rails of the container. However, a heaped or protruding load, which is common, will tend to prevent or hinder the extension of the tarp over the container. As a result, the operator will be required to climb on the container to either lift the tarp over the heaped or protruding portions of the load or to right a pull bar which may have been directed off the top edges of the containers by the load and fallen into the container. Hence, a high risk of injury exists with these systems as well.